Drugs and the Brain in General Psychology

General Psychology Course

  • Instructor: Matt Junker, Ph.D.
  • Course Term: Spring 2026

Topic: Drugs and the Brain

How Drugs Work

  • Mechanism of Action:
    • All psychoactive drugs affect neurotransmission through neurotransmitters.
    • Neurotransmission Process:
    • Neuron depolarizes (becomes more likely to fire) or polarizes (becomes less likely to fire).
    • Neurotransmitters are released into the synaptic gap after neuron firing.
    • Types of Neurotransmitters:
      • Excitatory Neurotransmitters: Increase the likelihood that a receiving neuron will fire.
      • Inhibitory Neurotransmitters: Decrease the likelihood that a receiving neuron will fire.

Agonists Mimicking Neurotransmitters

  • Many drugs act as agonists, mimicking neurotransmitters:
    • Heroin/Morphine:
    • Bind to opioid receptors, where endorphins typically bind.
    • Effects: pain relief (painkiller), sedation, euphoria.
    • Typically have an inhibitory effect.
    • Nicotine:
    • Binds to acetylcholine receptors, which are involved in cognitive functions like memory and attention.
    • Acetylcholine is active within the mesolimbic pathway, closely associated with the dopamine reward pathway.
    • Vital for all rewarded learning processes, such as food location and mate selection.

Link Between Addiction and the Mesolimbic Pathway

  • Addiction is related to the mesolimbic (reward) pathway:
    • Includes dopamine-sensitive neurons across various areas.
    • Projects to the Ventral Tegmental Area (VTA), where nicotine also binds.
    • Increases dopamine release, impacting cognitive control and decision-making.
    • Inputs from the Amygdala and Hippocampus play a role in implicit learning.

Understanding Excessive Phone Use

  • Can increased phone use be viewed through this lens?
    • Is the phenomenon a matter of reduced attention span or potential behavioral addiction?

Other Substances Mimicking Neurotransmitters

  • LSD & Psilocybin:

    • Mimic serotonin, which is essential for excitatory neurotransmission, predominantly in the prefrontal cortex.
    • Promote the release of glutamate, a key general excitatory neurotransmitter across the brain involved in synaptic plasticity.
    • Both substances suppress the default mode network engaged in self-referential thinking, leading to increased brain connectivity but decreased organization.

  • Tetrahydrocannabinol (THC):

    • Binds to cannabinoid receptors, primarily inhibitory receptors found in the hippocampus, cerebellum, amygdala, and frontal cortex.
    • THC inhibits GABA, which is responsible for inhibiting dopamine release, resulting in paradoxical effects: simultaneous inhibition in certain areas coupled with euphoria from increased dopamine.
    • Major areas affected include:
    • Limbic System: regulates emotions and memory.
    • Emotional responses may become exaggerated and misinterpreted leading to paranoia and disconnect from context around emotions.

Blocking Reuptake of Neurotransmitters

  • Some drugs interfere with the reuptake process of neurotransmitters post-receptor binding:
    • Selective Serotonin Reuptake Inhibitors (SSRIs):
    • Function to increase serotonin levels within the synaptic gap.
    • Cocaine:
    • Blocks dopamine reuptake, permitting that more dopamine remains in the synaptic gap, enhancing its effects.

Increasing Efficiency of Receptors

  • Benzodiazepines (e.g., Xanax):
    • Bind to specific sites on GABA receptors and amplify their sensitivity to GABA, enhancing inhibitory effects.
  • Barbiturates:
    • Share similar actions enhancing the effects of GABA.

Blocking Ion Flow into Cells

  • Ketamine:
    • Primarily used in anesthetic contexts.
    • Binds to NMDA receptors (which are excitatory) within the ion channel to block ion influx.

Multifaceted Drug Effects

  • Ecstasy:
    • Prevents reuptake of serotonin, dopamine, and norepinephrine.
    • Displaces serotonin from neurons, potentially damaging them, leading to post-use depressive episodes.
  • Alcohol:
    • Highly impactful, particularly on the hippocampus:
    • Enhances GABA effects, resulting in increased inhibitory action.
    • Inhibits glutamate, leading to reduced excitation.
    • Boosts dopamine levels.

Discussion Activity

  • Group Activity:
    • Participants to write all names on paper and form groups with at least one member who has watched the corresponding Ted Talk.
  • Discussion Topics on Addiction:
    • Explore impressions of the Ted Talk and its conclusions regarding addiction.
    • Debate if social/environmental factors primarily influence addiction decisions.
    • Assess whether addiction is solely determined by current environmental contexts and provide justification.

Withdrawal and Addiction

  • Withdrawal symptoms and the phenomenon of addiction can also be attributed to neurotransmission alterations:
    • Suppressed neurotransmitter production.
    • Fewer available receptor sites leading to decreased dopamine system effectiveness.
    • Opponent Processes:
    • The body develops compensatory mechanisms against drug use leading to withdrawal symptoms, such as:
      • Depression during stimulant withdrawal.
      • Anxiety during alcohol withdrawal.
      • Physical pain during opioid withdrawal.

Conclusion

  • Express gratitude for student participation and attention throughout the lecture.